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\DOC choose
\TYPE {choose : ('a, 'b) func -> 'a * 'b}
\SYNOPSIS
Picks an arbitrary element from the graph of a finite partial function.
\DESCRIBE
This is one of a suite of operations on finite partial functions, type
{('a,'b)func}. These may sometimes be preferable to ordinary functions since
they permit more operations such as equality comparison, extraction of domain
etc. If {f} is a finite partial function, {choose f} picks an arbitrary pair of
values from its graph, i.e. a pair {x,y} where {f} maps {x} to {y}. The
particular choice is implementation-defined, and it is not likely to be the
most obvious `first' value.
\FAILURE
Fails if and only if the finite partial function is completely undefined.
\EXAMPLE
{
# let f = itlist I [1 |-> 2; 2 |-> 3; 3 |-> 4] undefined;;
val f : (int, int) func = <func>
# choose f;;
val it : int * int = (2, 3)
}
\SEEALSO
|->, |=>, apply, applyd, combine, defined, dom, foldl, foldr,
graph, is_undefined, mapf, ran, tryapplyd, undefine, undefined.
\ENDDOC
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